Leslie Armstrong-Lea wrote- Seeing these posts about safety precautions to be used while >pregnant and working in flow cytometry prompted me to send a word of >caution to ALL flow cytometrists, pregnant or not. We all need to be >careful when using toxic, carcinogenic, pathologic, etc. samples or >chemicals. We tend to get so used to working with this stuff, that I >think we forget to respect the potential hazards. > I was diagnosed with thyroid cancer last year, and although the >only "known" cause of thyroid cancer is radiation exposure (which I >have not had), the nuclear medicine doctor that administered my >ablative dose of I131 following my surgery was curious about my >exposure to propidium iodide for 15 years. Even though it is not >supposed to be taken up by live tissue,, he did wonder if it could >cause thyroid cancer, as the thyroid has such an affinity for iodine of >any sort. I don't know if anyone would have any answers to this, but I >just wanted to make sure everyone, not just pregnant ladies, respects >the warnings to use caution when dealing with dyes, chemicals, body >fluids, etc. Be safe out there!! Yes, the thyroid does have an affinity for iodine, but propidium iodide is a salt, with the organic molecule propidium as the cation and iodide as the anion. There is no covalent bond between the propidium and the iodine, meaning that if propidium iodide were to get into the body, the thyroid could take up the iodide, and the propidium would associate itself with some other anion, but the thyroid would be no more likely to take up propidium than would any other organ. And propidium is not taken up readily by eukaryotic cells with intact membranes. According to Molecular Probes' Material Safety Data Sheet, propidium is not listed as a carcinogen although it is known to be mutagenic in microorganisms - and it *can* get into viable microorganisms under some circumstances (it would have to in order to be mutagenic). So it seems unlikely that your thyroid cancer was related to propidium exposure. But I would not recommend getting your minimum daily requirement of 150 ug of iodine in the form of propidium iodide, either. I endorse your safety recommendations; I treat dyes and other reagent chemicals the same way I treat wild mushrooms; I know some of them are edible, and some are poisonous, and, since I'm not absolutely sure which are which, I don't eat any of them. And I did go to medical school and was trained in medical oncology before I became a flow jock, so I am not wandering hopelessly far from my area of expertise here. -Howard
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